Question

Can anybody explain me this statement!

pin.sin_addr.s_addr = ((struct in_addr *)(hp->h_addr))->s_addr;

Answer 1

Takes hp->h_addr, and casts it to struct in_addr*. The cast may have different reasons. Perhaps hp->h_addr is void* and the cast is needed to tell the compiler what type it should use for finding s_addr. It may also be another struct that has an in_addr as its first member

struct in_addr {
  struct saddr_t s_addr;
};

struct socket {
  struct in_addr addr;
};

struct server {
  struct socket *h_addr;
};

server *hp;

Then, casting socket* to in_addr* would be valid because on its address there is a in_addr at the beginning. After the cast, the member s_addr is accessed. These types are common in network programming under POSIX, and don’t look like in my above example, but the above could have been the situation at hand.